device-context

Arguments: window

Returns an integer that identifies the device-context of window if it has one, or nil otherwise. A device-context is a construct used in the Windows API to specify a set of parameters that are used when drawing on a window. A common graphics application does not normally need to deal with a window's device-context directly, but if you need to pass the window to a winapi function that calls for the window's device-context (or hDC), then you should pass the integer returned by this function for that argument. See also windows:handle, which returns the window's "handle".

Every non-control window in common graphics (and every lisp-widget window) is automatically assigned a device-context, which it keeps until it is closed. Controls supplied by the OS (all controls except lisp-widgets), on the other hand, are not automatically given device-contexts in lisp since it is normally only the OS rather than lisp that draws on the control. If you do want to draw directly on a non-lisp control, then you must give the window of the control a device-context while drawing on it. The easy way to do this is to wrap a call to with-device-context around the code that draws on the control.

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This page was not revised from the 8.1 page.
Created 2010.1.21.